TST/FIX: ArchiveSearchWidget & TraceFileConvert Tests

[zdomke]

Adding tests for ArchiveSearchWidget and ArchiveResultsTableModel.

Fixing issues that came up during testing:

• In config.py & config.json:
  • Remove archiver_urls because I realized they aren't being used anywhere in the project and could cause confusion
• In archive_search.py:
  • Change the method of getting the logger to prevent getting a duplicate
  • Fix ArchiveResultsTableModel.rowCount implementation because it requires an argument when it should default to an empty QModelIndex
  • Populate ArchiveSearchWidget.archive_url_textedit with $PYDM_ARCHIVER_URL instead of hardcoding the URL
  • In ArchiveSearchWidget.request_archiver_info, make some wildcards work for 1+ characters instead of just 1 character

[zdomke]

Note:
Tests for default model values and model validity will fail with the current version of PyDM (at the time of writing this) as some PyDM models will still return empty QVariants when a request is invalid. I have already made a PR for this: slaclab/pydm#1122

Second Note:
Some other test may fail due to a bug in FormulaCurveItems. I already have a PR to fix this bug as well. We can ignore tests with the same error message as the PR:
slaclab/pydm#1124

[zdomke]

Adding tests for TraceFileConvert.

Additional fixes that came up during testing

• In plot_config.py:
  • Convert legend_chckbx.stateChanged signals to bool because it caused an issue in exported files
• In trace_file_convert.py:
  • Improve remove_null_values
  • StripTool files with no curves throw a ValueError
  • Fix error with imported formula colors in Java Archive Viewer files